1. Field of the Invention
This invention relates to a device for integrally controlling an engine and an automatic transmission in a vehicle.
Automatic transmissions for vehicles, having gear shift mechanisms, a plurality of frictionally engaging devices, and hydraulic control devices operated to selectively switch the engagements of the frictionally engaging devices so that any one of a plurality of gear stages can be achieved, are well known in the transmission art.
In general, the frictionally engaging device is comprised of two sets of friction plate elements which are relatively rotatably supported and a hydraulic servo device for driving the friction plate elements. When oil pressure is fed to the hydraulic servo device, the two sets of the friction plate elements are strongly urged together so that both sets of the friction plate elements are frictionally engaged with sufficient force to transmit torque therebetween.
In general, the working oil pressure to the frictionally engaging devices is a line pressure. This line pressure has heretofore been controlled in accordance with a value to be regarded as typifying an engine load, such as for example, a throttle opening of the engine. More specifically, the control is carried out such that the line pressure increases with increasing engine load.
In the past, line pressure control was carried out such that throttle oil pressure which varied with the throttle opening was introduced into a control port of a primary regulator valve for controlling the line pressure. In such prior art embodiment, throttle oil pressure is generated by a throttle valve, which has a resilient force increasing with increasing accelerator pedal depression. In recent years, an electronically-driven automatic transmission has been developed, whereby essential portions of a control circuit are formed by an electronic circuit. In the electronically-driven automatic transmission of this type, information on the throttle opening is processed in the form of an electric signal, whereby the line pressure is controlled in response to an electric signal relating to the throttle opening (For example, in Japanese Utility Model Kokai (Laid-Open) No. 125555/1981).
In recent years, so-called superchargers have been attached to engines to improve the power characteristics thereof. Such superchargers deliver increased quantities of gasified fuel-air mixture to the cylinders of the engine, thereby raising the mean effective pressure during combustion so that output is improved for a given rotary speed. Known superchargers are driven by two methods: a mechanical driving method and an exhaust gas turbine driving method. The mechanical driving types utilize the rotational force of a crankshaft or the like of the engine, and are generally designated superchargers. The exhaust gas turbine driving types utilize engine exhaust gas energy and are generally designated turbochargers.
The intake air pressure flowing into the engine cylinder from the supercharger is known as the boost pressure. In general, when the boost pressure is excessively high, knocking tends to occur in gasoline engines, and durability is reduced in diesel engines. Consequently, boost pressure is typically controlled by a waste gate valve and an actuator so that the boost pressure can be normally held at a preset value. Although increasing boost pressure gives rise to increasing engine output, the fuel consumption is increased accordingly, whereby the fuel consumption rate is deteriorated. Because of this, there recently has been developed an engine system equipped with a supercharger, wherein this boost pressure is gradually or continuously changed in an active manner based upon the various operating conditions of the engine, so that a selective running may be performed with the emphasis being placed on output or fuel conservation.
However, when the engine boost pressure is continuously or gradually changed as described above, for a particular throttle opening or the engine speed, the engine torque inputted into the automatic transmission varies continuously or gradually. Conventional automatic transmissions cannot cope with this properly. Further, the output of supercharged engines fluctuates greatly with the intake air temperature, as compared to the normal aspirate engine. Because of this, if the operational intake air temperature is assumed to be low and the oil pressure in a hydraulic control device of an automatic transmission is thus set at a rather high value, then during operation at high intake air temperatures, shift shock increases due to the high value of the oil pressure. In the reverse case, if the operational intake air temperature is assumed to be high and the oil pressure is thus set at a relatively low value, then during operation at lower intake air temperatures, shift time duration will increase due to the low oil pressure, and wear of the frictionally engaging devices increases. To summarize the above, in supercharged engines, the degree of fluctuation of an engine output due to the change in the intake air temperature is combined with the degree of fluctuation of an engine output due to the change in the boost pressure, such that when the intake air temperature is high and the boost pressure is low, then shift shock is high. Furthermore, when the intake air temperature is low and the boost pressure is high, then the burden (work to be done) by the frictionally engaging devices is increased.